Get some Denatured alcohol or 91% Isopropyl alcohol.
WEAR LATEX or EQUIVALENTGLOVES!! you don't want body oils to get on the inside of the platter or the idler wheel.
On the platter there may be a circlip (C-clip) holding it down. Remove and lift the platter straight UP.
Clean the inner surface of the platter top to bottom. Set aside.
Look at the idler wheel and check for cracking, grazing, hardness, etc. The rubber wheel should be nice and supple with no glazing on the edge, no hardness on the edge, no cracks, etc.
Can you post a pocture of this Turntable.? It would help immensely .
While you have the platter off, take a paint brush and dust the whole thing. Then lubricate the spindle bearing with some light machine oil *sewing Machine oil. Do the motor bearings also.